1. Field of the Invention
This invention relates to valves. More specifically, the present invention is directed to a switching valve for controlling the direction of flow of fluids by the use of piezo-electric elements as actuators and to an electro-pneumatic pressure converter utilizing the switching valve for process control and other applications.
2. Description of the Prior Art
Electromagnetic valves utilizing an electrically energized solenoid coil have been used conventionally for controlling the direction of flow of fluids such as air, water, etc. However, in systems where high speed switching was required in spite of low fluid flow rates, means other than the above described electromagnetic switching valves were not generally available for attaining required high switching speeds. Although the electromagnetic valves did realize smooth, accurate and speedy control of fluids, they had an inherent problem of relatively high electric driving power consumption. Particularly in cases where the flow rates were ralatively low and the switching frequencies were relatively low at 10 to 20 Hz, the driving power was still relatively large, making high power consumption a serious drawback.
Since fluid switching operations must be carried out at relatively high speeds in devices using pulse modulation for controlling the flow and pressure of fluids, the need for a simple switching valve other than the above described electromagnetic valve has been felt for a long time.
In conventional electro-pneumatic pressure converters, electrical input signals were converted into fluid pressure signals by converting the electrical signals into a fluid nozzle back pressure. In one such device, a piezo-electric element was used on a nozzle flapper, and the nozzle flapper installed to face a nozzle opening was moved in response to the input signal to change the gap between the nozzle opening and the flapper to regulate the nozzle back pressure. In another such device, the gap between the nozzle flapper and the nozzle opening was not controlled but instead the nozzle flapper was arranged to oscillate near the oscillation frequency, and the ratio between the full nozzle open and full nozzle closed time during one cycle was regulated in response to the input signal. However, in both the above devices a serious drawback was that sufficient gain could not be obtained for the input signal while converting the electrical input signal into nozzle back pressure.